Transmission circuits



Jan. 1, 1924 1,479,505

K. S. JOHNSON TRANSMISSIQN CIRCUITS Filed Jan; 1 6 1920 Harmer/7 ida/mson Patented Jan. 1, 1924-.

UNITED STATES 1,479,505 PATENT OFFICE.

KENNETH S. JOHNSON, OF JERSEY CITY, NEW JERSEY, ASSIGNOR T0 WESTERN ELEG- TRIC COMPANY, INCORPORATED, YORK.

OF NEW YORK, N. Y., A CORPORATION OF'NEW TRANSMISSION CIRCUITS.

Application filed January 16, 1920. Serial No. 351,944.

To all whom it may concern:

Be it known that l, KENNETH S. JoHN- SON, a citizen of the United States of America, residing at Jersey City, in the county of Hudson and State of New Jersey, have invented certain new and useful Improvements in Transmission Circuits, of which the following is a full, clear, concise, and exact description.

This invention relates to loading systems and more particularly relates to means for loading three wire transmission systems.

As described in my copending application, Serial No. 321,889, filed September 5, 1919, it is frequently desirable toemploy in transmission systems, such as telephone systems, a three-wire transmission circuit in preference to the usual two-wire or fourwire circuit. In the usual operation of a three-wire transmission circuit, the transmission in one direction is accomplished over the two outside wires used serially,

while transmission in the opposite direction is accomplished over the two outside wires in parallel using the central branch as the return wire. r

It is well known'in the art that the transmission characteristics of a signaling circuit are considerably improved by inserting lumped impedances in the line at periodic intervals, thereby loading the circuit.

In loading a two-wire circuit, it is customary to insert at the proper points in the circuit, inductances in equal amounts in both of the line wires, thereby keeping the two sides of the circuitbalanced with respect to ground. It is also customary to wind both of these inductances on the same of the three line'wires would not be feasible since such a connection would permit crosstalkto be present to such an extent as to render the circuit inoperative." Furthermore the loading would not be the same for j transmitting currents in either direction. The circuit would also be unbalanced with respe'ctjto ground.

1 In accordance with this invention, these objections to the loading of the three-wire circuit have been overcome by providing separate inductances for loading the'circuit for transmission in both directions and by that the inductances which load the circuit for transmission in one direction offer negligible impedance to transmission in the opposite direction. In the preferred form this is accomplished by employing at each loading point two separate loading coils. The inductance coil which loads the circuit for transmission over the two outside wires serially, requires only two windings, one in each of the two outside wires. The inductance coil which loads the circuit for transmission over the two outside wires in parallel requires three windings one in each of the three wires.

This invention will be better understood by reference to the following detailed description taken in connection with the accompanying drawing which represents this invention embodied in a three-wire transmission circuit, connected between two telephone sub-stations. Referring to the drawing, the transmission circuit comprises the two outside line wires 3 and 4: and a central wire 5. The

'two outside wires. 3 and 4: are connected to windings 6 and 7 of induction'coils 8 and 9 of sub-stations A and B respectively. The central wire 5 is connected to the mid-points of windings 6 and 7 Sub-station A' comprises a transmitter 11 in circuit with a battery 12 and the input of a repeater 13. The output of repeater 13yis connected in circuit with a battery15 and the primary winding of induction coil 8. The receiver 16 of sub station A is connected serially in the central wire 5.

Sub-station B comprises a transmitter 21 in circuit with a battery 17 and the input of a repeater 18. The output of repeater 18 is connected serially in central wire 5 of the transmission circuit. The receiver-19 of the sub-station set is connected in circuit with the secondary wmdmg of transformer 9.

Current for the three wire transmission circurrents by transformer 8 areimpressed on i the twooutside wires 3 and 4 of the transmission circuit. No current flows through the central wire 5, since the central Wire is connected to the mid-point of winding 6. The amplified currents from repeater 13 will therefore be impressed on receiver 19 by transformer 9 of sub-station set B without there being any substantial side-tone present in receiver 16 of sub-station A.

When transmitting from sub-station B to sub-station'A, the signaling currents from transmitter 21 are amplified by repeater 18 and the amplified currents are impressed on a circuit for which the eentralwire 5 constitutes one side, and outside wires 3 and 4: in parallel constitute the other side. Since for transmission in this direction thecurrents are flowing in parallel over wires 3 and 4, the signaling currents from transmitter 21 are impressed on receiver 16 without there being any substantial side-tone in the receiver 19. r

In order to improve the transmission characteristics of such a three-wire circuit, it

'may be desirable to load the circuit at a plurality of points therein. In the drawing two inductance coils 25 and 26 are shown for loading the circuit at one point andinductance coils 27 and 28 are shown for loading the circuit at another desired point. Inductance coil 25 comprises windings 30 and 31 inserted in the wires 3 and i in such a mariner that the direction of the flux producedin the two coils is shown by the arrows adjacent thereto, that is, the impedancesoi' windings'30 and 31 should be aiding for currents flowing serially through the outside wires 3 and 1 Inductance coil 27 is similar to inductance coil 25 and has two windings 32 and 33 in the circuit so arranged that-their impedances areaiding for currents flowing serially through wires 3 and 4. However, for currents flowing in parallel through wires 3 and 1, the flux for the two windings of each of the coils 25 and 27 would be equal and opposite so that their impedances would be substantially zero for currents flowing in the stated direction.

Inductance coil 26 comprises three wind- 'ings '35, 36 and 37 in wires 3, 5 and i respectively. The direction of the flux in the three windings as shown by. the arrows should be such that the impedances of the three windings are aiding for currents which traverse wires 3and 4 in parallel and re turn over line wire 5. Since the direction of the'fiux is the same for windings 35 and 37, the two windings will ofier a negligible impedance for currents flowing serially through wires 3 and 4. Inductance coil 28 is similar to inductance coil 26 and has three windings38,39 and 40'inserted in the circuit similar to windings 35, 36 and 37 of coil 26. i i

- As shown in the drawing, loading coils 25,

26, 27 and 28 may be of the well-known -toroidal type although it is obvious that this invention .is not limited inits application to loadihg systems employing only that Y type of'loading coil.

By loading the circuit in the above described manner, crosstalk may be prevented, the tAIGQ-WllB circuit is kept balanced with respect to ground and the loading for both directions may be made the same. It is preferable that windings 30 and 31 should be wound on a diiierent core from windings 35, 36 and 37 as this reduces to a considerable degree the chances for cross-talk in the circuit.

It is to be understood that the embodiment of this invention as described above may be variously modified without departing in any wise from the spirit of this invention as defined in the appended claims.

The phrases .outside branches and central conducting path as used in this specifi cation and the appended claims, are intended to refer to the electrical relation of the three wires rather than to their, geographical position withrespect to each other.

What is claimed is: 1

1J1n an electric system, a transmission circuit comprising two outside branches and a central conducting path, means for loading said circuit for transmission in one direction over said two outside branches in series relation, and means for loading said circuit for transmission in the opposite direction over said branches in parallel returning over said path. e

2. A three wire transmission circuit loaded for transmission in both directions at periodic intervals thereof, the three wires of said circuit being balanced with respect to ground. v

3. A three wire transmission circuit and means for loading said circuit for transmission in both directions at a proper interval thereof, while preventing any. appreciable amount of cross talk between the three wires of said circuit. V Y I I 4. A three wire transmission circuit, and means for loading said circuit equally at a proper interval thereot for transmission currents in either direction. 7

5. In an electric system, a transmission circuit comprising a'pluarlity of line wires in which transmission at one time is carried on serially through two of said wires, transmission at another time being carried on; through said two wires in parallel returning over the third of said wires, and means for loading said circuit at both times without unbalancing said circuit. 7

6. In an electric system, a transmission circuit comprising a plurality of line wires in which transmission at one time is carried on serially through two of said-wires, the

transmission at another timebeing carried onthrough said two wires in parallel returning over a third of said wires, andmeans for loading said circuit at both times with-' out producing cross-talktherein.

In an elect sy em a r nsmi si circuit comprising a plurality of line Wires in which transmission at times is carried on serially through two of said wires, the transmission at other times being carried on through said two Wires in parallel returning over a third of said wires, an impedance inserted in said circuit at a proper interval thereof for loading said circuit for trans mission at said certain times, and a second impedance at said interval for loading said circuit for transmission at said other times.

8. In an electric system, a transmission circuit comprising three line wires in which transmission in one direction is carried on serially through two of said line wires, the transmission in the opposite direction being carried on through said two wires in parallel returning over the third of said wires, an inductance coil inserted at a proper interval of said circuit for loading said circuit for transmission in one direction and an inductance coil inserted at said interval for loading said circuit for transmission in the opposite direction.

9. In an electric system, a transmission circuit comprising three line Wires in which transmission in one direction is carried on serially through two of said line wires, the transmission in the opposite direction being carried on through said two of the line wires in parallel, returning over the third of said wires, a two winding inductance coil and a three winding inductance coil inserted in said circuit at a proper interval thereof for 8 loading said circuit, said two winding inthrough said branches, transmission at an other time being carried on through said branches in parallel returning over said path, and means for loading said circuit at both times without unbalancing said circuit.

11. In an electric system, a transmission circuit comprising two outside branches and a central conducting path in which transmission in one direction is carried on serially through said branches, the transmission in the opposite direction being carried on through said branches in parallel returning over said central path, a two-winding inductance coil and a three-winding. inductance coil inserted in said circuit at a proper interval thereof for loading said circuit, said two-winding inductance coil having a winding in each of said branches, said threewinding inductance coil having a winding in said path and in each of said branches.

In witness whereof, I hereunto subscribe my name this 13th day of January A. D., 1920.

KENNETH s. JOHNSON. 

